1. Field of the Invention
This invention relates to improved panel clinching methods. The term "clinching" is also known as "press joining" or "integral fastening".
2. Prior Art
Spot welding is the most commonly used technique for joining vehicle body components in the automotive industries. As the strength of each spot weld cannot be guaranteed, eg. due to the inclusion of rubbish between the components, or poor weld penetration, designers must increase the number of welds to ensure adequate joint strength.
Spot welding has not yet been developed as an accurate, reliable method for joining galvanized steel or aluminum components.
With galvanized steel, welding action destroys the galvanized about the weld site, making it liable to corrosion.
Aluminum has great potential in the automobile field due to its light weight, but the lack of a suitable spot welding method is one reason which has minimized its application.
One alternative to spot welding is the use of self-piercing rivets, and a method of, and apparatus for, the fastening of metal panels with self-piercing rivets is disclosed in U.S. Pat. No. 4,615,475 (Fuhrmeister) (International Publication Number WO 84/04710).
A further alternative method is metal clinching, where two sheets of metal are deformed into a locking engagement using a punch-and-die combination. Examples of metal clinching methods are disclosed in:
1. DE 4009813 (Fraunhoffer-Ges Ford Ange); PA1 2. DE 1452820 (Philips Patentverwaltung GmbH); PA1 3. DE 3726392 (Kuka Schweissanlage); PA1 4. EP 330061 (Eckold W. & Co GmbH); PA1 5. EP 215449 (Rapp E.); PA1 6. GB 2244946 (Fairacre Limited); PA1 7. GB 2123734 (BTM Corporation); PA1 8. U.S. Pat. No. 3,919,955 (Du Vernay); and PA1 9. U.S. Pat. No. 387,599 (Ladouceur et al). PA1 a hollow rivet or full tubular slug is driven or inserted into a clinched joint and at least the inner end of the shank of the rivet or slug is outwardly-deformed within the joint.
While these methods enable metal sheets to be joined together, they have relatively low shear and axial load strengths, and the joints do not have an outer face substantially flush with the surrounding sheet metal (and are therefore not applicable in exposed areas, eg. within an engine compartment).